1. Field of the Invention
This invention relates to power gas burners of the gun type. The invention is disclosed herein as it may be applied to gas burners of the type that may be utilized with domestic heating furnaces and other domestic appliances having capacities not in excess of about 400,000 B.t.u. per hour. It is to be understood, however, that the invention may be adapted to other services and uses and to burners of greater capacity.
2. Description of the Prior Art
Power gas burners of the gun type are well known in the art. Such burners embody an air tube and a blower which supplies both primary and secondary combustion air to the burner. The primary air is supplied to a mixing means where it is mixed with the gas which is supplied at a regulated pressure, the mixing means ordinarily being disposed within an air tube to which the secondary air is supplied by the blower. Prior burners have employed blowers of the squirrel cage type that produce a pulsating discharge with a resultant pulsating flame and noise, and a reduced combustion efficiency as compared to non-pulsating flames.
The present invention relates to burners of the flame-retention type embodying a flame-retention burner head disposed at or near the end of the air tube. The fuel, which has been mixed with the primary air, is discharged from the mixing means at or near the burner head and is ignited immediately downstream of the burner head. The burner head creates a zone in which the forward velocity of the air and fuel mixture is less than the rate of flame propagation. The base of the flame remains adjacent to the burner head. A burner head of this type is disclosed and claimed in my copending application Ser. No. 092,221, filed Nov. 7, 1979, now U.S. Pat. No. 4,278,406 which specifically discloses an oil burner embodying a burner head of this type.
Power gas burners are advantageous as compared to conventional gas burners in which natural draft is relied upon to supply the secondary air and in which the mixing of the gas with the primary air is accomplished by the velocity of the gas as it is discharged from an orifice connected to a supply of gas under presssure. If power gas burners are accurately controlled, they are able consistently to provide mixtures of fuel and air at very near stoichiometric proportions and in this respect they are superior to atmospheric burners. The more accurate proportioning of gas and air flow results in higher combustion temperatures and reduces the number of square feet of heat transfer surface required for a given capacity as compared to atmospheric burners. The proper proportioning of air and gas supply also increases the rate of combustion, reduces the size of the flame, and reduces the residence time of the gas and air in the flame. These factors all combine to reduce contaminants in the flue gases such as CO and NO.sub.x.
A power gas burner of the gun type is illustrated in the Delancey and Cooperrider U.S. Pat. No. 3,820,943, issued June 28, 1974. This patent illustrates a burner embodying a conventional squirrel cage type blower which discharges air into an air tube. Gas is supplied by a tube leading to the center of the air tube and the velocity pressure at the periphery of the blower wheel, rather than the static pressure in the air tube, is utilized by means of a scoop that deflects air into the gas tube through a slot in the wall thereof. The gas is thus partially premixed with the air that is deflected by the scoop into the gas tube. This patent also discloses a burner head disposed at the end of the air tube. The burner head is centrally apertured to receive the end of the gas tube.
The Levey et al U.S. Pat. No. 2,077,424 illustrates a pressure gas burner having a conventional proportional mixer of the inspirator type for mixing the primary air with the gas. A burner head having primary air-fuel mixture ports and secondary air ports is illustrated. The mixer supplies a rich mixture of primary air and fuel to the burner ports. This burner depends upon the velocity of the gas emitted from a nozzle into the mixer to mix the gas and primary air, and would be sensitive to changes in atmospheric and combustion chamber pressures. The patent contemplates that changes in the ratio of primary air to fuel will take place, and these changes are said to be compensated for by corresponding changes in the quantity of secondary air made available. Other power gas burners are illustrated, for example, in the Conway U.S. Pat. No. 3,180,394, issued Apr. 27, 1965, the Vorheis et al U.S. Pat. No. 3,391,981, issued July 9, 1968, and the Wolffradt U.S. Pat. No. 2,966,347, issued Dec. 27, 1960.
In general, the prior art patents of which I am aware do not appear to provide burners that will operate at substantially constant air-fuel ratios under varying conditions, nor are the prior art burners readily adaptable to efficient operation under different firing rates and in conjunction with different types and sizes of furnaces.